The invention relates to an electrical power supply system for an automobile vehicle.
The electrical power supply for an automobile vehicle is provided using an accumulator battery charged by an alternator, usually driven by a vehicle traction engine.
Most automobile vehicles now use a battery outputting a voltage of 12 V and the corresponding alternator outputs a voltage of 14 V. Since the number of items of equipment consuming electrical energy onboard automobile vehicles is increasing, the power output by the battery also needs to increase. It is becoming quite frequent for each vehicle to be provided with a computer and electrical controls, particularly for the adjustment of seats, assisted braking, suspensions, etc.
The power of a battery with a given voltage (12 V) is proportional to the output current. But an increase in the current also increases the cross section of the power supply cables, which a non-negligible extra cost. This is why the use of accumulator batteries with a higher voltage (36 V) is being considered for the power supply of electrical power sources onboard automobile vehicles. These batteries must be charged at a voltage of 42 V. A voltage of 36 V is high enough to give a substantial power increase without any current increase, and it is also sufficiently low so as not to endanger users.
But in the automobile industry where equipment is produced in large production series, it is difficult to consider changing from one standard to another without a transition, for cost reasons. This is why it is probable that equipment such as lights, computer(s) and small motors will continue to be used with a low voltage (12 V) power supply during a relatively long transition period, and that the high voltage will be used for equipment necessitating more power such as starting, braking, suspensions, etc. Furthermore, for the same cost reasons it would be preferable to be able to continue using low voltage alternators, particularly 14 V, during the transition period, to charge the 12 V and 36 V batteries. Therefore, a circuit is necessary such that the conventional alternator outputting a voltage of 14 V can supply a voltage of 42 V to charge the 36 V battery.
A power supply system for an automobile vehicle has already been proposed by which an alternator outputting a voltage of 14 V could charge a 12 V battery and a 36 V battery. A circuit of this type is shown in FIG. 1.
This known circuit comprises a battery 10 that outputs a voltage of 12 V, a battery 12 outputting a voltage of 36 V, and a three-phase alternator 14 outputting a voltage of 14 V to charge these two 5 batteries. The alternator is of the claw or Lundell type. In this known circuit, a voltage of 42 V can be applied at the terminals of the battery 12 through a voltage boost circuit, that takes advantage of the high internal inductance in each phase of the alternator 14. Each phase terminal 14i, 142 and 143 the alternator 14 is connected to the common anode point of a first diode 16i to the cathode of a second diode 18i, the cathode of the diode 16i being connected to the xe2x80x9cplusxe2x80x9d terminal of the battery 12 and the anode of the diode 18i being connected to the xe2x80x9cminusxe2x80x9d terminal (and therefore the ground) of the same battery 12 outputting a voltage of 36 V. A controlled switch 20i installed in parallel on each of the diodes 18i.
Furthermore, each phase terminal 14 is connected to 20 the plus terminal of the 12 V battery 10 through another controlled switch 22i.
Thus, the circuit shown in FIG. 2 is obtained for each alternator phase; the alternator 14 supplies power firstly to the battery 10 (12 V) through the inductance 24i phase i and the controlled switch 22i, and secondly to the battery 12(36 V) through a diode 16i. A switch 20i placed between firstly the point common to the inductance 24i the anode of the diode 16i, and secondly the ground to which the negative terminals of the batteries 10 and 12 and one terminal of the alternator 14 are connected.
Operation is illustrated by the diagrams in FIGS. 3a, 3b and 3c. The ordinate of the diagram in FIG. 3a represents the intensity I L of the current in the inductance 24i, and the abscissa represents the time t, while the diagrams in FIGS. 3a,3b and 3c also show the intensity 136 of the charge current of battery 12 (FIG. 3b) and the intensity 112 of the charge current of the 12V battery 10 (FIG. 3c)
During a first period with duration xcex11T (FIG. 3a), the switch 20i is closed. Under these conditions, the alternator 14 charges inductance 24i and the intensity IL reaches an intermediate value Int starting from a minimum value Imin. During a second phase, the switch 20i is opened and the switch 22i is then closed. Under these conditions, the voltage at the terminal s of battery 10 is the sum of the voltage from this battery and the voltage output by the inductance 24i at continues its charge into the battery 10.
After time xcex12T, the switch 22i is open. Under these conditions, the diode 16i arts conducting since its anode voltage is greater than the cathode voltage and thus the alternator 14 supplies power to the 36 V battery 12 through the charged inductance 24i. The battery 12 is powered until a time T at which the intensity IL reaches the value Imin (FIG. 3a).
The invention is based on the realisation that there are two disadvantages with the circuit shown in FIG. 1. Firstly this circuit is expensive because two controlled switches have to be supplied per phase and the control is complex. Secondly, there is a period from 0 to xcex11T during each control cycle that is unused for charging either of the batteries.
The invention overcomes these disadvantages.
It relates to an electrical power supply system for a vehicle that comprises a multiphase alternator outputting a given voltage and that will charge a battery with a voltage lower than this given voltage and a battery with a higher voltage. This system comprises a single directional switch for each phase of the alternator through which power is supplied to the low voltage battery, and it is characterised in that the power supply for the battery with a voltage greater than the alternator voltage is not provided with a controlled switch and in that means are provided to control each switch preferably at a frequency significantly greater than the alternator frequency, such that during each control period the switch is closed for a first fraction of the period during which the low voltage battery is charged at the same time that the corresponding phase of the alternator is charged, and is open during a second period during which the higher voltage battery is charged.
With this circuit, only one controlled switch is necessary per phase, and the first fraction of a switch control period is used entirely for charging the lower voltage battery and the second fraction is used entirely for charging the higher voltage battery.
Thus, in general, the invention relates to an electrical power supply system for an automobile vehicle comprising an alternator, a first battery with a voltage less than the electromotive force or the nominal voltage of the alternator, a second battery with a voltage higher than the electromotive force or nominal voltage of the alternator, and control means such that the first battery is charged while the inductance internal to the alternator is being charged and such that the second battery is charged while this internal inductance is being discharged. This system comprises a combination of the following:
for each alternator phase, a controlled switch in series with the first battery with a lower voltage, and a diode means to charge the second higher voltage battery, and
control means for each controlled switch such that 20 when each controlled switch is closed, the first battery is charged at the same time as the inductance of the corresponding phase of the alternator, and when the controlled switch is opened after the inductance is charged, it discharges into the second battery.
Preferably, the charge circuit of the second battery does not have a controlled switch.
According to one embodiment, the control means are such that each switch operates at a frequency significantly greater than the operating frequency of the alternator. For example, this control frequency of the controlled switch may be of the order of ten times the operating frequency of the alternator.
According to one embodiment, the control means are such that the fraction of each control period of the controlled switch during which the controlled switch is closed depends on the alternator rotation speed.
The system may comprise a filter capacitor between the cathode of the diode means and the ground. In one embodiment, the system comprises a filter capacitor between a terminal of the controlled switch and the ground.
In one embodiment, the voltage of the first battery is of the order of 12 V, the voltage of the second battery is of the order of 36 V, and the alternator voltage is of the order of 14 V.
As a variant, the voltage of the first battery is of the order of 12 V, the voltage of the second battery is of the order of 36 V and the alternator voltage is of the order of 28 V.
For example, the alternator may be of the claw or Lundell type.